1. Field of the Invention
The present invention relates to a current sensor that measures the magnitude of current, and more particularly, to a current sensor capable of reducing noise from disturbance magnetism.
2. Description of the Related Art
In recent years, in fields such as an electric vehicle and a solar battery, a current value that is involved has been increased due to increases in output and performance of the electric vehicle or the solar battery device, and a current sensor that contactlessly measures a high DC current has been widely used. As such a current sensor, a sensor including a magnetic sensor that detects a current to be measured, which flows through a conductor, using a change in magnetic field in the periphery of the conductor has been suggested. In addition, as the current sensor, a current sensor that reduces noise from disturbance magnetism has been developed.
As the current sensor that reduces noise from disturbance magnetism, a current sensor which acquires a differential between output signals of a pair of magnetic sensors disposed on the same substrate has been suggested (for example, refer to Japanese Unexamined Patent Application Publication No. 2002-243766). In the current sensor, the pair of magnetic sensors are disposed on the substrate at positions that oppose each other with a current line interposed therebetween, which is orthogonal to the substrate. The sensing axis directions of the pair of magnetic sensors are the same direction. In the current sensor, since the output signals having reversed phases to each other are output from the pair of magnetic sensors, the output signals are processed to be added to each other by differential operation and thus output sensitivity is enhanced. In addition, noise components other than the output signals of the pair of magnetic sensors have the same phase and thus are removed by the differential operation.
However, in a case where the magnitude of current for driving the motor of an electric vehicle is measured by the current sensor, the current to be measured becomes a high current during motor driving and becomes a minute current during motor stoppage. Therefore, a current sensor capable of measuring both the high current and the minute current with high accuracy is preferable. In addition, with an expansion of applications of the current sensor in recent years, further reductions in the size and the thickness of the current sensor are preferable. In terms of the reductions in the size and the thickness of the current sensor, it is preferable that the magnetic sensors be disposed in the vicinity of the current line.
However, in the current sensor described in Unexamined Patent Application Publication No. 2002-243766, in the case where the pair of magnetic sensors are disposed in the vicinity of the current line, there is a problem in that the pair of magnetic sensors become magnetically saturated by an induction magnetic field from the current to be measured, which flows through the current line. Particularly, in a case where the current to be measured which is an object of measurement is a high current, the induction magnetic field from the current to be measured is increased, and thus the magnetic sensors are likely to become magnetically saturated. As such, in the current sensor according to the related art, it is difficult to realize both the measurement of the current to be measured, which is a high current, and the reductions in the size and the thickness of the current sensor.